The following references are believed to represent the state of the art:
US Published Patent Application 2003/0149621 of Shteyn;
US Published Patent Application 2003/0149975 of Eldering, et al.;
US Published Patent Application 2005/0216932 of Danker;
US Published Patent Application 2006/0031892 of Cohen;
US Published Patent Application 2006/0218602 of Sherer, et al.;
US Published Patent Application 2008/0235087 of Amento, et al.; and
US Published Patent Application 2008/0282285 of Thomas, et al.